Bellows for sliding constant velocity joints

ABSTRACT

A convoluted boot for sealing an annular gap between two parts which are connected to one another in a rotationally fast way, which can be articulated relative to one another and which are axially displaceable relative to one another, especially of a constant velocity plunging joint, consisting of includes a low-strain polymer hard material having a first larger collar ( 11 ) to be secured to a first component, a second smaller collar ( 12 ) to be secured to a second component and a plurality of annular fold units which extend between the first collar and the second collar. and which, in the form of The outer folds consisting of have two annular flanks ( 31, 32 ), and form a fold peak ( 21 ) between two fold valleys ( 22 ). In a first group (A) of at least three annular folds with a connection to the first collar  11  annular folds, the diameters of the fold peaks ( 21 ) and fold valleys ( 22 ) decrease in the direction from the first collar to the second collar. In a second group (B) of annular folds with a connection to the second collar  12  of at least one fold, the diameters of the fold valleys and, optionally, of the fold peaks ( 21 ) are constant. The ratio of the diameter (D 1 ) of the fold peak ( 21 ) of the largest annular fold (A 1 ) of the first group (A) to the diameter (D 2 ) of the second collar ( 12 ) is greater than or equal to 2.5.

The invention relates to a convoluted boot for sealing an annular gapbetween two parts which are connected to one another in a rotationallyfast way, which can be articulated relative to one another and which areaxially displaceable relative to one another, especially of a constantvelocity plunging joint, consisting of a low-strain hard polymermaterial, having a first larger collar to be secured to a firstcomponent, a second smaller collar to be secured to a second componentand a plurality of annular fold units which extend between the firstcollar and the second collar and which are provided in the form of outerfolds which consist of two annular flanks and each form a fold peakbetween two fold valleys.

Because requirements become more and more stringent, convoluted boots ofsaid type are produced from hard polymer materials to an increasingextent. As compared to soft resilient materials used earlier, said hardpolymer materials feature an improved resistance in mechanical andchemical respects, and in view of higher speeds and the need for alonger service life, it is inevitable that they are used. One concern istheir reduced flexibility which can be a problem at low temperatures. Inthe case of constant velocity fixed joints which effect articulationonly between two rotating components, convoluted boots made of saidmaterials, even today, do meet the respective requirements in theirentirety. In the case of constant velocity plunging joints which, inaddition to the angular movement, effect an axial displacement betweenthe two rotating components, this means that the sealing convolutedboots are subject to friction contact between the annular flanks on theinside of the angle when the joint is in a telescoped and articulatedcondition and, when the joint is in the extended and articulatedcondition, the individual annular folds open up excessively widely onthe outside of the angle, causing a collapsing of the annular folds orother irregularities. At high speeds, in particular, this can result inthe elasticity limit of the convoluted boot being exceeded and it canlead to boot damage.

It is therefore the object of the present invention to provide aconvoluted boot of said type which is able to meet more stringentrequirements in operation without suffering any damage and which istherefore particularly suitable for constant velocity plunging joints.The objective is achieved by providing a convoluted boot of theinitially mentioned type with the following characteristics:

-   -   in a first group of annular folds joining the first collar with        at least three annular folds, the diameters of the fold peaks        and fold valleys decrease from the first collar to the second        collar,    -   in a second group of annular folds joining the second collar        with at least one annular fold, the diameters of the fold        valleys and—if more than one present—of the fold peaks are        constant,    -   the ratio of the diameter D₁ of the fold peak of the largest        annular fold of the first group to the diameter D₂ of the second        collar amounts to ≧2.5;    -   the two annular flanks of each of the annular folds of the first        group (A) form angles extending in opposite directions with a        radial plane (R), wherein a smaller angle β is formed by the        annular flank pointing to the second collar and wherein a larger        angle α with α≧β+25° is formed by the annular flank pointing to        the first collar;    -   the annular flanks of each of the annular folds of the first        group (A), which annular flanks point to the first collar, are        curved so as to be outwardly convex.

By providing two special groups of folds, the deformation of theconvoluted boot when articulation and changes in axial length occur isallocated to said two groups in such a way that, in the first groupconsisting of folds of a decreasing size, deformation largely takesplace in the form of the articulation of the individual annular flanksrelative to one another, whereas the second group consisting of at leastone annular fold with a smaller diameter largely accommodates the changein axial length as a result of the at least one annular fold beinglengthened. The convex shape of the annular flanks stabilises theannular folds of the first group in respect of being bent inwardly andlargely prevents the annular flanks of the individual annular folds ofthe first group from rubbing against each other.

Convoluted boots with two different groups of folds are known from DE 3309 386 C1, DE 43 23 686 C2, DE 196 01 096 A1 and DE 198 06 173 C1 forexample. However, in these cases, between the two groups of folds, thereexists a region which is in constant contact with the inserted shaft.From DE 38 73 496 T2, there is known a convoluted boot of said type withtwo different functional regions, having folds whose flanks extendparallel relative to one another and, on the outside, are connected toone another by a rounded annular bead.

From U.S. Pat. No. 5,236,394 there is known a convoluted boot of saidtype wherein there is formed a transition fold with a fold peak and afold valleys with smaller diameters relative to the correspondingdiameters of the remaining annular folds, wherein the fold valleys ofthe transition fold, first, are to establish a supporting contact with ashaft shank if the convoluted boot is arranged at a universal joint andwhen this is articulated.

The annular folds according to the present invention, however, when thetwo collars are coaxially aligned relative to one another in the fittedcondition, are contact-free relative to the inserted shaft and theannular folds each, approximately, comprise the shape of a double cone.

The first group of folds can comprise up to five annular folds and thesecond group of folds can comprise up to eight annular folds. The numberof folds depends on the respective requirement profile regarding theangle of articulation and the change in length. It is obvious that withan increased number of annular folds, the need for a longer boot lengthalso increases, but the angle work to be carried out by the individualfolds generally decreases during articulation. However, this does notaffect the possibility of varying the shape of the individual foldswithin certain ranges, i.e. that it is possible to provide more pointedand wider folds, but in principle, the folds of the first group arewider (have a larger volume) and the folds of the second group are morepointed (narrower).

According to a preferred embodiment it is proposed that between thefirst collar and the first annular fold (A1) of the first group (A)there is positioned a joining region whose greatest outer diameter,substantially, is not greater than that of the first collar and that thegreatest outer diameter of the first annular fold (A1) of the firstgroup, in turn, substantially, is not greater than that of the joiningregion In this way, it is possible to observe small installationdimensions.

Furthermore, it is proposed more particularly that the annular flanks ofeach of the annular folds of the second group form opposed angles with aradial plane, wherein the annular flank pointing towards the secondcollar forms an angle β and wherein the annular flank pointing towardsthe first collar forms an angle α which is defined by α=(β±5°).

As the approximately conical annular flanks of the annular folds of thefirst group, which point towards the first collar, are curved so as tocomprise a convex outside, it is specified hereby that the reference forthe angle values has to be the conical face between the outercircumferential line of a fold valley and the outer circumferential lineof a fold peak and that, if viewed in a longitudinal section, it has tobe the straight line between the smallest outer radius of a fold valleyand the greatest outer radius of a fold peak.

According to a further embodiment it is proposed that between theannular folds of the first group and the annular folds of the secondgroup, there is provided a transition fold whose diameters at the foldvalleys deviate from one another, wherein the diameter of the annularflank pointing towards the first collar is greater than the diameter ofthe annular flank pointing towards the second collar. In particular, itis proposed that the annular flanks of the transition fold form opposedangles with a radial plane, wherein the annular flank pointing towardsthe second collar forms an angle β and that the annular flank pointingtowards the first collar forms an angle α which is defined by(β+25)≧α≧(β+5°). Said transition fold is thus similar to the annularfolds of the first group in that the diameter of the fold valleysdecreases towards the second collar; however, as far as the angleconfiguration of the annular flanks is concerned, said transition foldis similar to the annular folds of the second group. The purpose is toensure that even at larger angular movements of the convoluted boot,there is preferably no friction contact between the fold valleys and theinserted shaft.

According to a preferred embodiment, the diameter of the fold peak ofthe transition fold (C) is smaller than or equal to the diameter of thefold peak of the adjoining annular fold of the first group (A) andgreater than or equal to the diameter of the fold peak of the adjoiningannular fold of the second group (B). Furthermore, it is advantageousfor the diameters of the fold valleys of the transition (C) to besmaller than the diameters of the fold valleys of the annular flanks ofthe first group (A) and greater than the diameters of the fold valleysof the annular folds of the second group (B). As a result, when theuniversal joint associated with the convoluted boot is articulated, thetransition fold remains contact-free for a longer period of time orcompletely, relative to an inserted shaft shank.

A preferred material for the convoluted boot is a thermoplasticelastomer (TPE); in particular, there are proposed materials based onpolyurethane (TPU), on polyester (TPEE), in particular a polyether esteror a polyester ester, materials based on polyamide (TPA) or onpolyolefin, in particular polypropylene or polyethylene.

A preferred embodiment of the convoluted boot in accordance with theinvention will be described below with reference to the drawings wherein

FIG. 1 shows an inventive convoluted boot in half a longitudinalsection, with different individual characteristics having been drawn in.

FIG. 2 shows an illustration similar to that of FIG. 1 in which thedimensions specified by the invention are given.

FIG. 3 shows two annular folds in half a longitudinal section, givingthe values of the angles.

FIG. 1 shows a convoluted boot comprising a first collar 11 with alarger diameter with an attaching region 11′ whose greatest outerdiameter, substantially, is not greater than that of the first collar, asecond collar 12 with a smaller diameter with a joining region 12′, aswell as a total of seven complete annular folds. A first group Acomprises three annular folds A1, A2, A3, with the diameters of theirfold valleys and fold peaks decreasing from fold to fold from the firstcollar 11 to the second collar 12. A second group B of two completefolds B1 and B2 and with a total of three fold peaks comprises foldvalleys and fold peaks which comprise identical diameters. A thirdtransition fold C is positioned between the first group A and the secondgroup B and comprises fold valleys with decreasing diameters from thefirst collar 11 to the second collar 12. At fold A1 it is indicated thata complete annular fold is regarded as an outer fold with a fold peak 21between two fold valleys 22.

In FIG. 2, any details identical to those shown in FIG. 1 have beengiven the same reference numbers. To that extent, reference is made tothe preceding description. D₁ refers to the outer diameter of the firstfold A1 of the first group A and D₂ refers to the outer diameter of thesecond collar 12. In accordance with the invention, the ratio of the twodiameters D₁/D₂ is ≧2.5.

FIG. 3 shows an individual fold, and in FIG. 3 a, one fold, which can befold A1 for example, comprises a first annular flank 31 and a secondannular flank 32. A radial plane R is positioned normally on thelongitudinal boot axis L. The opening angle of the first annular flank31 relative to the radial plane R has been given the reference symbol aand the opening angle of the second annular flank 32 relative to theradial plane R has been given the reference symbol β. FIG. 3 b showsthat at an annular flank (31) with a convex outer face or, optionally,at an annular flank (32) with a concave outer face, the arm of theopening angle α deviating from the radial plane is formed by a straightline between the greatest circumferential line 41 of the fold peak andthe smallest circumferential line 42 of the adjoining fold valley. FIG.3 a shows that the arm of the opening angle β deviating from the radialplane is formed by a strictly conical surface of the annular flank (32)itself.

1.-16. (canceled)
 17. A convoluted boot for sealing an articulatable andplungeable joint, comprising: a low-strain hard polymer material; afirst larger collar (11) for securing to a first component; a secondsmaller collar (12) for securing to a second component; and a pluralityof annular fold units which extend between the first collar and thesecond collar and which comprise outer folds having two annular flanks(31, 32) forming a fold peak (21) between two fold valleys (22); whereinthe fold units form a first group (A) of at least three annular foldsjoining the first collar (11), the diameters of the fold peaks (21) andfold valleys (22) decreasing in the direction from the first collar (11)to the second collar (12), and a second group (B) of at least oneannular fold joining the second collar (12), the diameters of the foldvalleys (22) and the fold peaks (21) of the second group (B) beingconstant; and wherein the two annular flanks (31, 32) of each of theannular folds of the first group (A) form opposed angles with a radialplane (R), wherein a smaller angle (β) is formed by the annular flank(32) pointing towards the second collar (12) and wherein a larger angle(α) with α≧(β+25°) is formed by the annular flank pointing towards thefirst collar (11), and the annular flanks (31) of each of the annularfolds of the first group (A) which point to the first collar (11) arecurved so as to be outwardly convex; and wherein a ratio of a diameter(D₁) of the fold peak (21) of the largest annular fold (A1) of the firstgroup (A) to a diameter (D₂) of the second collar (12) is ≧2.5.
 18. Aconvoluted boot according to claim 17, wherein the first group (A)comprises up to five annular folds.
 19. A convoluted boot according toclaim 17 comprising, between the first collar (11) and the first annularfold (A₁) of the first group (A), a joining region (11′) whose greatestouter diameter is substantially equal to that of the first collar (11).20. A convoluted boot according to claim 17, wherein the second group(B) comprises up to eight annular folds.
 21. A convoluted boot accordingto claim 18, wherein the second group (B) comprises up to eight annularfolds.
 22. A convoluted boot according to claim 20, wherein the annularflanks (31, 32) of each of the annular folds of the second group (B)form opposed angles with a radial plane, wherein the annular flank (32)pointing towards the second collar (12) forms a first angle (β) andwherein the annular flank (31) pointing towards the first collar (11)forms a second angle (α) which is defined by α=(β±5°).
 23. A convolutedboot according to claim 21, wherein the annular flanks (31, 32) of eachof the annular folds of the second group (B) form opposed angles with aradial plane, wherein the annular flank (32) pointing towards the secondcollar (12) forms a first angle (β) and wherein the annular flank (31)pointing towards the first collar (11) forms a second angle (α) which isdefined by α=(β±5°).
 24. A convoluted boot according to claim 17comprising, between the annular folds of the first group (A) and theannular folds of the second group (B), a transition fold (C) whosediameters at the fold valleys (22) deviate from one another, wherein thediameter of the fold valley at the annular flank (31) pointing towardsthe first collar (11) is greater than the diameter of the fold valley atthe annular flank (32) pointing towards the second collar (12).
 25. Aconvoluted boot according to claim 22 comprising, between the annularfolds of the first group (A) and the annular folds of the second group(B), a transition fold (C) whose diameters at the fold valleys (22)deviate from one another, wherein the diameter of the fold valley at theannular flank (31) pointing towards the first collar (11) is greaterthan the diameter of the fold valley at the annular flank (32) pointingtowards the second collar (12).
 26. A convoluted boot according to claim24, wherein the annular flanks (31, 32) of the transition fold (C) formopposed angles with a radial plane (R), wherein the annular flank (32)pointing towards the second collar (12) forms a first angle (β) andwherein the annular flank (31) pointing towards the first collar (11)forms a second angle (α) which is defined by (β+25°)≧α≧(β+5°).
 27. Aconvoluted boot according to claim 25, wherein the annular flanks (31,32) of the transition fold (C) form opposed angles with a radial plane(R), wherein the annular flank (32) pointing towards the second collar(12) forms a first angle (β) and wherein the annular flank (31) pointingtowards the first collar (11) forms a second angle (α) which is definedby (β+25°)≧α≧(β+5°).
 28. A convoluted boot according to claim 24,wherein the diameter of the fold peak of the transition fold (C) is lessthan or equal to the diameter of the fold peak of the adjoining annularfold (A₃) of the first group (A) and greater than or equal to thediameter of the fold peak of the adjoining annular fold (B1) of thesecond group (B).
 29. A convoluted boot according to claim 26, whereinthe diameter of the fold peak of the transition fold (C) is less than orequal to the diameter of the fold peak of the adjoining annular fold(A3) of the first group (A) and greater than or equal to the diameter ofthe fold peak of the adjoining annular fold (B1) of the second group(B).
 30. A convoluted boot according to claim 24, wherein the diametersof the fold valleys of the transition fold (C) are less than thediameters of the fold valleys of the annular folds of the first group(A), and greater than the diameters of the fold valleys of the annularfolds of the second group (B).
 31. A convoluted boot according to claim26, wherein the diameters of the fold valleys of the transition fold (C)are less than the diameters of the fold valleys of the annular folds ofthe first group (A), and greater than the diameters of the fold valleysof the annular folds of the second group (B).
 32. A convoluted bootaccording to claim 28, wherein the diameters of the fold valleys of thetransition fold (C) are less than the diameters of the fold valleys ofthe annular folds of the first group (A), and greater than the diametersof the fold valleys of the annular folds of the second group (B).
 33. Aconvoluted boot according to claim 17, wherein the convoluted bootcomprises a thermoplastic elastomer (TPE).
 34. A convoluted bootaccording to claim 33, wherein the material comprises a TPE based on atleast one of a polyurethane (TPU), a polyester (TPEE), a polyamide(TPA), or a polyolefin (TPO).
 35. A convoluted boot according to claim34, wherein the TPEE is a polyether ester or a polyester ester.
 36. Aconvoluted boot according to claim 34, wherein the TPO is apolypropylene or a polyethylene.